The thief's original role was extremely entangled with how the g.m ran the game, with how they use traps, surprise, creature awareness, other classes ability to sneak or discover things etc.

And the backstab ability somehow grew into the idea of the thief as weedy but opportunistic super stabber.

I've never really like this, and also think it's weird having ambush and dirty tricks fighting styles not be a fighter thing.

As any professional murderer/soldier/gladiator/bruiser is going to take full and frequent advantage of any combat advantage they can.

It's only the (arguably mythologized) "chivalric knight" or "honourable samurai" that these techniques are a poor fit for.

Though a "warrior caste" class that is build around the central idea of it coming from a culture that has either heavily ritualised/ limited/controlled warfare or the caste is more about embodied of the values of the culture than military effectiveness .

There's more to be expanded on the idea of roles, where to split class, if they need to work ..together , etc.